50 million flights have been made on the London Eye since the observation wheel opened to the public in 2000.
Visitor number 50 million was among the Anderson family party visiting the South Bank attraction on Wednesday morning.
Staff greeted the Anderson family as they prepared to board and treated them to a special celebratory experience in their own private capsule.
It was an extra special experience for the Andersons as three generations of the family were at the London Eye, with visiting American grandparents Gregg and Sandy joining their UK-based son Eric, wife Heidi and their children Stefan, Caroline and Marta.
"To reach 50 million visitors since our opening in March 2000 is a testament to the popularity of the London Eye, a structure that has become one of the most recognisable and well-loved sights in the London skyline," said David Sharpe, divisional director of Merlin Entertainments.
"It is now as integral to the capital's silhouette as Big Ben, Tower Bridge and the Houses of Parliament and we are very proud to reach this milestone.
"London is the best city in the world and the London Eye is the best place to see it from; we are looking forward to welcoming the next 50 million guests in the years to come."